1. Field of the Invention
The present invention relates to a mobile communication system.
2. Description of the Related Art
At present, efforts are being made at 3GPP (3rd Generation Partnership Project) to study LTE (Long Term Evolution) and SAE (System Architecture Evolution).
One of the important themes in the study of 3GPP-LTE/SAE is addressed to the control of UPE Relocation (User Plane Entity Relocation). The control of UPE Relocation is the control of the switching of UPEs to which an UE (User Entity) is to be connected (see, for example, JP-A 2003-348661).
An UPE functional entity is an entity for handling user plane processing towards an eNB (eNodeB) or vice versa, and is defined in the core architecture of SAE. Examples of the UPE functional entity include paging initiation, heater compression, and encryption. The UPE functional entity may be located at a node in common with an MME (Mobile Management Entity) functional entity or a dedicated node.
An S1 interface between a core network and an access network interconnects the UPEs in the core network and the eNBs in the access network according to a full-mesh topology through an IP (Internet Protocol) network. Physically, therefore, the eNBs can connect to all the UPEs in a PLMN (Public Land Mobile Network). Even if the scope of eNBs to which the UPEs can be connected is logically limited and defined as the administrative scope of UPEs, an eNB can flexibly be connected to any one of the UPEs whose administrative scope covers the eNB.
An UE camped in LTE is connected to a single UPE at a certain point in time. The UPE to which the UE is connected changes by way of UPE relocation. Normally, UPE relocation takes place when UEs are in an idle mode (LTE_IDLE). The idle mode is a standby mode in which the UEs are not communicating. Though it is preferable for UPE relocation to be possible even in an active mode (LTE_ACTIVE) in which the UEs are communicating, such UPE relocation should be avoided as much as possible to circumvent the need for a complex relocation procedure.
The above related art suffers the following problems:
According to 3GPP-LTE/SAE, it is possible to connect the eNBs and the UPEs through the flexible S1 interface. It is not clear how to define UPEs and their administrative scope as well as how to limit the administrative scope of UPEs not to the entire PLMN, but to a portion thereof. In view of better user data communications, it should be taken into account how to reduce the frequency of UPE relocations that occur when the administrative scope of UPEs is limited.